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Abstract:

A flexible tool comprises stiffening means switchable in use from a first
state of relatively low stiffness to a second state of relatively high
stiffness, and subsequently switchable from the second state back to the
first state.

Claims:

1. A flexible tool, wherein the tool comprises stiffening means
switchable in use from a first state of relatively low stiffness to a
second state of relatively high stiffness, and subsequently switchable
from the second state back to the first state.

2. A tool as claimed in claim 1, in which the stiffening means comprise
thermoplastic or fibre-reinforced thermoplastic or low-melting-point
alloy or ultraviolet-curable adhesive.

3. A tool as claimed in claim 1, in which the stiffening means are
repeatably switchable between the first and second states.

4. A tool as claimed in claim 1, in which the switching is achieved by
the selective application of heat to the stiffening means.

5. A tool as claimed in claim 1, in which the switching from the first
state to the second state is achieved by the selective application of
ultraviolet light to the stiffening means.

6. A tool as claimed in claim 1, in which the tool comprises a plurality
of linked segments movable relative to one another, and the stiffening
means act in the second state to lock the links between segments and
prevent the relative movement.

7. A tool as claimed in claim 1, and further comprising remotely operated
control means to direct the flexing of the tool.

8. A tool as claimed in claim 7, in which the control means comprise
wires or hydraulic or pneumatic actuators or shape-memory alloy elements.

9. A tool as claimed in claim 7, and in which the tool comprises a
plurality of parts or segments that can be flexed independently.

10. A tool as claimed in claim 1, and further comprising a conduit (14)
extending longitudinally through the tool.

11. A tool as claimed in claim 1, and further comprising a gripping
segment that can be actuated to locate or secure the tool in use.

12. A tool as claimed in claim 11, in which the gripping segment is
inflatable.

13. A method of performing an operation using a flexible tool as claimed
in claim 1, the method comprising the steps of: inserting the tool into a
workspace; positioning the tip of the tool at a desired position in the
workspace; switching the stiffening means to the second state; performing
the operation; switching the stiffening means to the first state;
removing the tool from the workspace.

Description:

[0001] This invention relates to flexible tools of the sort sometimes
referred to as "snake-arm robots".

[0002] Snake-arm robots are commonly used to perform inspections and other
operations in hazardous or confined spaces, particularly where the nature
of the space or the presence of obstructions means that there is no
line-of-sight access to the region of interest within the space. Such
confined spaces exist in many different industrial environments, across a
wide range of technologies, for example in nuclear engineering, aircraft,
engines, industrial plants, shipbuilding, buildings, roads and pipelines.

[0003] Gas turbine engines are used for a number of purposes, including as
propulsion engines for ships and aircraft, to power pumps for gas or oil,
and for power generation.

[0004] When such engines are used on aircraft, they need periodic
inspection, maintenance and repair. It is possible to do this by removing
the engine from the aircraft and dismantling it, but there are serious
disadvantages in this approach. Gas turbine engines are complex machines
and their dismantling (and subsequent reassembly) is time-consuming and
expensive. In addition, to remove the engine from the aircraft is itself
a time-consuming and expensive procedure. While the engine is removed,
the aircraft cannot be used, which causes inconvenience and financial
loss to the operator. It has therefore become more common in recent years
to perform inspections, and where possible other operations, with the
engine still installed.

[0005] Engines are commonly provided with a number of ports in their outer
casings, through which inspection tools can be inserted. These tools
allow components within the engine to be inspected. In some cases,
inspection tools can also be manoeuvred through the front or rear of the
engine, between the blades and vanes. A very limited number of
maintenance and repair operations can also be carried out by introducing
specially adapted tools through the borescope ports. Among the operations
that are commonly carried out this way are borescope inspection,
penetrant inspection and ultrasonic inspection.

[0006] Because of the great advantages offered by in-situ inspection and
repair techniques, it would be desirable to be able to carry out a wider
range of operations using such tools. However, the scope of such
operations is limited by the dimensions of the borescope port (typically
less than 12 mm in diameter) and by the size of subsequent openings
inside the engine (e.g. between vanes). It can also be difficult, if not
impossible, to access the components furthest from the port because of
the tortuous routes and relatively long distances involved.

[0007] Flexible borescopes are known, which are similar in principle to
medical endoscopes, and these can be useful to reach less accessible
places within the engine. However, they can be floppy and difficult to
position accurately because of their reduced stiffness. Generally, such
devices require mechanical guides to direct them along a predetermined
path.

[0008] The flexibility of conventional robotic arms is provided by a small
number of discrete "elbows", at which rotational joints are provided.
This limits their flexibility, and restricts their usefulness in confined
spaces. Snake-arm robots (also sometimes referred to as continuum robots,
elephant's trunks, octopus arms, tentacles or drivable endoscopes)
comprise a large number of segments linked by rotatable joints, and they
are therefore more flexible than conventional robotic arms. Control wires
within the snake-arm robot are selectively joined to the segments to
allow independent control or steering of the separate segments. An
operator will typically "drive" the tip of the snake-arm robot through a
desired path in the confined space, and software will ensure that the
rest of the robot follows and does not foul on any obstructions within
the space. It is also possible to control the flexing of such a robot
joint-by-joint, or by reference to a Cartesian or other fixed coordinate
system.

[0009] Although snake-arm robots are known that are small enough to fit
through gas turbine borescope ports, their load-carrying capacity is so
small (typically of the order of a few grams for a robot 600 mm long)
that they are of no use for repair operations. Known snake-arm robots
with greater load-carrying capacity have correspondingly greater
diameters, and so can not fit through the borescope ports. Furthermore,
the longer a snake-arm robot is, the lower its load-carrying capacity at
the tip. Known snake-arm robots are therefore of no use to carry out such
in-situ operations.

[0010] The inventors have devised a snake-arm robot with a significantly
improved load-carrying capability, which will permit a much greater range
of inspection and repair operations to be carried out on installed
engines. Snake-arm robots according to the invention can also be made
longer than known robots, for a given load-carrying capacity.

[0011] The invention provides a flexible tool and a method of performing
an operation using a flexible tool as set out in the claims.

[0012] Embodiments of the invention will now be described, by way of
example, so that the way in which the invention is to be put into effect
may be better understood. Reference will be made to the accompanying
drawings, in which:

[0013]FIG. 1 shows a longitudinal cross-section of part of a flexible
tool according to a first embodiment of the invention;

[0014]FIG. 2 shows a transverse cross-section on the line A-A shown in
FIG. 1;

[0015]FIG. 3 shows part of the outer surface of the flexible tool of FIG.
1, with the covering layer partly removed; and

[0016] FIG. 4 shows a schematic illustration of a flexible tool according
to a second embodiment of the invention.

[0017] Referring first to FIGS. 1 and 2, a flexible tool according to the
invention, shown generally at 10, has a backbone 12 formed of a flexible
material such as a high-temperature-resistant silicone rubber. The
backbone 12 is tubular, and defines a central conduit 14. In use, this
conduit may accommodate an optical fibre bundle, tool drive cable or the
like 16. Spaced along the backbone 12 are radially extending projections
18 supporting a plurality of longitudinally spaced circular ribs 20. In
this embodiment, the radially extending projections 18 at each axial
position are equally spaced around the circumference of the backbone. It
is envisaged that the diameter of the tool is less than 12 mm, so that it
can fit through the borescope ports of a gas turbine engine.

[0018] The bending of the tool may be controlled in a known manner, as
follows. A plurality of sheathed control wires 22 run along the length of
the tool (only two are shown in FIG. 1), and through holes 24, 26 in the
ribs 18. The wires are free to move through the holes 24 and are guided
by them, in contrast to the holes 26 in which the wires are fixed in
place. In the embodiment shown, joints in the tool are effectively
defined by groups of four projections. The first projection fixes the
control wire from the previous joint in a hole 26, while control wires
for this and subsequent joints pass through a hole 24. The next two ribs
support and guide the control wires through holes 24, and the control
wire for this joint is fixed in a hole 26 in the fourth rib of the group.

[0019] Considering the four projections indicated in FIG. 1 as 18a, 18b,
18c, 18d, the wire 22 is fixed in hole 26 in projection 18d, but free to
move through holes 24 in projections 18a, 18b and 18c. Therefore, by
pulling on the wire 22, the projections 18a, 18b, 18c, 18d are pulled
closer together, causing a part of the backbone 12 to bend as shown. By
suitable control of the plurality of wires 22 any group of four
projections 18 can be similarly controlled, and therefore (because the
projections 18 extend in different radial directions from the backbone
12) any part of the backbone can be caused to bend in a desired
direction, In this way, generally under computer control, the tip of the
tool can be steered through obstructions in a workspace to reach the
region of interest, and the following parts of the tool can be steered as
necessary to follow the tip without fouling the obstructions.

[0020] This control mechanism allows the tip of the flexible tool 10 to be
steered to any desired position within a workspace, and to avoid
obstacles. In use, the tip of the flexible tool would accommodate
suitable tools to perform the desired inspection or operation. Such tools
may include an optical probe, a light source or a machining tip (driven
by a flexible drive shaft carried through the central conduit of the
flexible tool).

[0021] However, as indicated above, if known snake-arm robots are made
small enough to fit through the access spaces of a gas turbine engine
then their load-carrying capacity will be inadequate to perform the
desired operations; load-carrying capacity is relevant both in terms of
the ability to support the weight of the tools and to resist forces
generated during, for example, a grinding operation. Conversely, if their
load-carrying capacity is increased then they will inevitably become too
large to fit through the available access spaces. The invention provides
a flexible tool small enough to fit into the limited spaces in a gas
turbine engine, but with sufficient load-carrying capacity to enable a
wider range of operations to be performed.

[0022] Referring again to FIGS. 1 and 2, in a flexible tool according to
the invention the spaces between the projections 18 and ribs 20 are
filled with a cavity-filling medium 28. In the illustrated embodiment,
the medium 28 is a thermoplastic which is rigid at the normal operating
temperature of the tool. Around the outside of the tool 10, enclosing the
ribs 20 and medium 28, is an outer covering or skin 30, which
incorporates embedded heating elements. In FIG. 3, part of the skin 30
has been peeled back to show two heating elements 32.

[0023] In use, the heating elements 32 are controlled to heat the medium
28 above its glass transition temperature, so that it will melt or
soften. In this first state, the medium 28 will not impede the movement
of the tool 10 and so the tool may be bent (as described above) to permit
the tip to be driven through a workspace to a region of interest. The
medium will flow as necessary through the spaces between the projections
18 and ribs 20. A control mechanism may be provided so that, when the
medium 28 is in its first state and therefore behaving effectively as a
fluid, its pressure may be increased or reduced to control more precisely
the stiffness of the flexible tool. in general, a higher fluid pressure
will make the tool stiffer, and a lower fluid pressure will make it less
stiff. This more precise control may aid the deployment of the tool
within the workspace.

[0024] Once the tip of the tool is in the desired position, the heating
elements are switched off so that the medium 28 will cool. Once the
medium 28 cools below its glass transition temperature it will become
relatively rigid, and in this second state will effectively lock the ribs
20 and projections 18 in their positions. The entire tool effectively
becomes rigid. In this way, the tool 10 is provided with significantly
greater rigidity and therefore load-carrying capacity than similar known
tools. It is envisaged that, for a tool with a diameter of less than 12
mm, load-carrying capacities will be achievable in the order of 0.2 kg at
an overhang distance of 100 mm.

[0025] Once the inspection or repair operation is complete, the heating
elements 32 are again controlled to heat the medium 28 until it melts or
softens back into the first state, after which the tool 10 can be
withdrawn from the workspace.

[0026] In this way, a tool 10 according to the invention can be made small
and (in its first state) flexible enough to fit into confined spaces and
through small access ports, such as those in gas turbine engines, but at
the same time can be made (by switching into its second state)
sufficiently rigid to support appreciable loads, thereby enabling a much
wider range of inspection and repair operations to be performed, for
example without removing a gas turbine engine from the aircraft wing.

[0027] A further advantage may be gained if separate heating elements are
provided, spaced along the length of the tool 10. If these heating
elements are separately controlled, then it is possible to control the
stiffness of the tool segment-by-segment, or joint-by-joint, along its
length. This may facilitate the steering of the tool through difficult
areas of a workspace. Alternatively, it may allow parts of the tool to be
made rigid to allow operations to be performed, while keeping other parts
of the tool flexible; for example, to accommodate the movement of other
components.

[0028] In alternative embodiments of the invention, a different material
may be used for the medium 28. For example, it may be a fibre-reinforced
thermoplastic, or any other suitable material that can be made more or
less stiff by heating and cooling, for example a low-melting-point alloy.
It will be understood that the comments above (for example, concerning
segment-by-segment control of the tool) would apply equally to such
embodiments, with the necessary changes being made to the switching
mechanism.

[0029] In the embodiments described above, the stiffening and softening of
the medium 28 is a repeatable process. In a further alternative
embodiment, the medium is a UV-cured adhesive, and the tool is provided
with optical fibres or similar light-transmitting elements to carry UV
light to the medium when required. In its initial state, the adhesive is
soft and so the tool is flexible; once the tool is in the desired
position, UV light from a suitable source is directed into the medium to
cure it, rendering it stiff and locking the tool in position. After the
operations are completed, heat is applied to the adhesive (by embedded
heating elements as in the first embodiment described above, or by other
means) until the adhesive is degraded sufficiently to lose its stiffness.
The tool can then be withdrawn from the workspace. In such an embodiment,
the adhesive would not be re-usable; however, it may be possible to
remove the degraded adhesive and replace it with new adhesive for the
next use of the tool.

[0030] In alternative embodiments of the invention, the control of the
joints may be achieved by other means than by the control wires described
above. For example, hydraulic or pneumatic actuators may be provided, or
elements of shape-memory alloy may be provided in the joints which would
change their shape or dimensions when subjected to an electrical impulse.
It will be understood that such alternative actuators could also be
individually controlled.

[0031] In another alternative embodiment, not illustrated in the drawings,
instead of a single flexible backbone 12 a segmented backbone is
provided, with rotatable spherical-type joints between the segments. In
this embodiment, the medium acts when stiffened to lock the joints in
position, thereby providing rigidity to the tool.

[0032] FIG. 4 illustrates a further, optional feature of a tool according
to the invention, which may be combined with any of the embodiments
described so far.

[0033] In FIG. 4, a tool 10 according to the invention is shown within a
workspace. The tip 42 of the tool has been steered between two
obstructions 44. In a gas turbine engine, such obstructions may take the
form of blades or vanes.

[0034] Two inflatable gripping segments 46 are provided towards the tip of
the tool, one on each side of the tool. The segments may be formed
integrally with the skin of the tool, or may be formed separately and
stitched or otherwise attached to the skin.

[0035] When the tip of the tool is in the desired position the gripping
segments 46 are inflated, as shown in FIG. 4, to support the tool between
the obstructions 44. This provides a support for the tool relatively
close to its tip, thereby increasing the effective stiffness of the tool.
It means that the stiffness of the tool in use is not dependent on the
overall length of the tool, but only on the "overhang" between the
support and the tip. This enables longer flexible tools to be
constructed, to reach more inaccessible workspaces, without sacrificing
the rigidity of the tool or its load-carrying capacity.

[0036] When the operations have been completed, the gripping segments are
deflated so that the tool can be removed.

[0037] Other configurations of gripping segments may be used, depending on
the particular requirements of the application. For example, a single
annular gripping segment or a number of segments spaced around the
circumference of the tool. Gripping segments may be provided in multiple
positions along the length of the tool, as required.

[0038] The gripping segments may also be used for different purposes,
enhancing the capabilities of the flexible tool. For example, if the
inflatable segments are inflated to secure the tool between two rotatable
blades of a gas turbine engine, manual rotation of the engine could then
be used to "pull" the tip of the flexible tool to a different position,
further around the rotational axis of the engine. In this way, the
flexible tool may provide access to regions even further inside the
engine and even more remote from the access ports.

[0039] It will be appreciated that alternative designs of gripping
segments could be used, which would provide the same advantages as the
inflatable segments described above. For example, one or more
mechanically- or electrically-actuated gripping segments could be used,
which would be folded away within the body of the tool to permit its
insertion or removal, and deployed outwards from the body to provide
support when required.

[0040] The invention may also be applied in a simpler flexible tool, in
which the control mechanism for the flexing of the tool is absent or is
provided only along part of the length of the tool, for example in the
region near to the tip. The cavity-filling medium and its associated
softening/stiffening mechanism would still be present. Such a tool would
be cheaper and simpler to manufacture, and would still provide the
advantages of stiffness and load-carrying capacity associated with the
embodiments described in more detail above.

[0041] Elements of the invention, namely the cavity-filling medium and the
gripping segments, may be applied to other designs of snake-arm robots
and the like, as well as to those designs specifically described in this
specification.

[0042] The invention provides a flexible tool to facilitate access to
confined or hazardous spaces, but with a greatly enhanced load-carrying
capacity compared with known snake-arm robots. The additional
load-carrying capacity permits operations such as grinding or deburring
to be performed, which have previously been impossible because the tip of
the tool has not had sufficient rigidity to react the loads involved.